The main components of ice cream include water, sugars and fat. Butter oil is most commonly used as the fat ingredient in ice cream. Vegetable oils are also applied in ice creams, coconut oil being most commonly used. Coconut oil offers the advantage that, like butter oil, it has a relatively high solid fat content at low temperatures (e.g. between 5 and 10° C.) and a relatively low solid fat content at elevated temperatures, e.g. between 30 and 35° C. Furthermore, coconut oil contains relatively small amounts of unsaturated fatty acids, which means that it does not easily oxidise. The relatively small amount of unsaturated fatty acids found in coconut oil also constitute a serious drawback as it is generally accepted that oil that are low in unsaturated fatty acids do not fit in a healthy diet. The same holds true for butter oil, be it to a slightly lesser extent.
The use in ice cream of vegetable fat compositions, other than coconut oil, has been suggested in a number of prior art publications. U.S. Pat. No. 5,756,143 describes an interesterified triglyceride composition that contains relatively high amounts of polyunsaturated fatty acids, but that displays better oxidation stability than non-interesterified triglycerides with similar compositions. In the US patent an ice cream product is described that contains a fat blend that is composed of 90 wt. % palm oil and 10 wt. % of an interesterified blend of: 55 wt. % of a tuna oil olein fraction; 35 wt. % of high oleic sunflower oil; and 10 wt. % of sunflower oil. It is shown in the patent that the tuna oil olein fraction contains more than 50% ω-3 unsaturated fatty acids by weight of the total amount of fatty acids. These ω-3 unsaturated fatty acids are extremely rapidly oxidised to volatile aldehydes that impart a pronounced ‘fishy’ flavour. ω-3 unsaturated fatty acids may be present in the fat of the present food product in a concentration of up to 1.5 wt. % without giving rise to unacceptable flavour formation.
GB 1 444 820 is concerned with food fats containing palm and lauric fats that are suitable for use in ice-cream. The fat compositions taught by the British patent have an iodine value of 30-50, a slip melting point of 37-45° C. The fat compositions disclosed in the British patent are characterised by a saturated fatty acid content of more than 60 wt. %.
The abstract of JP 55 153561 refers to ice creams comprising a fat blend that contains 50-0 wt. % milk fat and 50-100 wt. % of fat consisting of (i) 50-100 wt. % of the medium melting point fraction of palm oil and (ii) 50-0 wt. % of other fat.
It would be desirable to replace coconut oil and butter oil in ice cream by oils that contain substantially larger amounts of unsaturated fatty acids. However, the use of such oils in aerated food products, such as ice cream, is associated with serious problems as these oils are easily oxidised. Oxidation of unsaturated vegetable oils leads to objectionable off-flavours that are often described as ‘cardboard-like’. Aerated food products containing unsaturated oils are particularly vulnerable to fat oxidation as they comprise a very large oil-air interface.
It is known that the oxidation stability of vegetable oils may be improved by hydrogenating these oils. Hydrogenation removes double bonds from unsaturated fatty acids, making them much less vulnerable to oxidation, especially if the oil is fully hydrogenated, in which case it contains only saturated fatty acids. However, hydrogenation also affects the melting characteristics of the oil. The melting behaviour of vegetable oils that have been hydrogenated to a considerable degree (e.g. fats with a melting point of more than 50° C.) is often found to be unsatisfactory. In addition, consumers increasingly object to the use of hydrogenated oils food products, especially if these hydrogenated oils contain appreciable amounts of trans fatty acids.
Consequently, there is a need for fats that contain substantial amounts of unsaturated fatty acids and that can suitably be applied in aerated food products without giving rise to serious off-flavour problems.